It is so easy for something like this to happen. My cat Sadie, whom I adored, went missing one day. It was several hours before we realized that we hadn't seen her in what was too long a time. After a while, we heard her crying, coming from behind my very large dresser. But it was muffled - and we couldn't understand why. We moved the dresser, and found the large patch in the drywall where the plumber had been earlier in the day to fix some pipes. Sadie had apparently wandered into the hole - it had never occurred to us that she might wander in, or that no one would notice her going in - and the plumber had walled her in. Thank goodness, she was able to find her way exactly to where she entered, and make herself heard, so that we could free her. She went through so many of her lives - more than nine, I think - she was such an overly-adventurous cat. Some of her adventures could have been prevented if she had been an indoor cat, as all of mine since have been. But that one - that was a fluke. Of course, I would know now to closet my cats away if a plumber was going to open a wall - but I didn't even know he was going to do that. I can't remember - it might even have been that he was doing the work while we were not at home, because I lived in a rented apartment at the time.